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6                                    POTABLE WATERS

The result, expressed as CaC03 per litre, represents the permanent
alkalinity (due to magnesium carbonate and alkali carbonates).

Finally, the difference between the two above alkalinities represents
the temporary alkalinity, that is, the calcium existing as bicarbonate, which
is precipitated as carbonate during boiling.

4. Ammonia.—This is determined by means of Nessler's solution
prepared by dissolving 50 grams of potassium iodide in 50 c.c. of hot water
and gradually pouring into this solution concentrated mercuric chloride
solution until the red precipitate begins to refuse to redissolve (20-25 grams
of mercuric chloride are required). To the filtered liquid is added a solution
of 150 grams of potassium hydroxide in 150 c.c. of water, the total volume
being made up to a litre with distilled water ; 5 c.c. of the concentrated
mercuric chloride solution are then added and the liquid shaken and allowed
to stand, the clear liquid being decanted into a bottle which is kept tightly
stoppered with a rubber bung and in the dark.

One hundred c.c. of the water are poured into a glass cylinder with a
ground stopper and 0-5 c.c. of sodium hydroxide solution (i : 2) and I c.c,
of sodium' carbonate solution (27 : 5) added. The liquid is shaken and
then allowed to stand, the clear liquid being decanted from the deposited
precipitate into another glass cylinder and treated with 1-2 c.c. of Nessler
reagent. The formation of a reddish-yellow turbidity or precipitate indi-
cates that the water contains ammonia, the amount of the latter increasing
with the intensity of the turbidity or precipitation.1

5.  Nitrous Acid (Nitrites) .-—Nitrites are detected by Grids's reagent,
comprising:    (i) saturated a-naphthylamine hydroehloride solution,   (a)
saturated sulphanilic acid solution, and (3) 10% pure hydrochloric or sul-
phuric acid solution.

From 10 to 50 c.c. of the water are introduced into a glass cylinder with
a ground stopper, 3 drops of the sulphanilic acid solution, i. drop of the
hydrochloric or sulphuric acid, and 3 drops of the a-naphthylamme hydro-
chloride solution being successively added. The presence, of nitrite, in the
Water is indicated by a coloration varying between rose red and deep
red according to the proportion.2

6.  Nitric Acid (Nitrates).—The qualitative test for nitrates may be
made with the ordinary reagent consisting of ferrous sulphate and sul-
phuric acid, the water being used as such or after concentration to a small

Traces of nitric acid may be detected by means of brudno : 2-3 c.c.
of the water are treated in a porcelain dish with a crystal of brucine and
a few drops of concentrated sulphuric acid free from nitric acid ; the presence
of nitrates in the water is shown by a red coloration rapidly changing to
greenish-yellow. For the quantitative determination, see Complete Analysis


7.  Phosphoric Acid (Phosphates),—>io c.c. of the water, either as

such or after concentration, are acidified with nitric acid, treated with

1 If comparison is made with standard ammonium chloride solutions, the quantity
of ammonia (or ammonium salts) in the water may be calculated.
a This method may similarly be rendered quantitative.  _         .    ai-